A multimedia broadcast multicast service (MBMS) is a service in which a plurality of base stations (BSs) transmit the same downlink signal in a single frequency network (SFN) system. The MBMS can obtain an SFN combining gain between cells by performing a multicast broadcast single frequency network (MBSFN) operation. The SFN combining gain denotes a diversity gain obtained in a receiving end by transmitting the same information for each cell without an extra operation. When the plurality of BSs transmit the same signals, the same signals transmitted from multiple cells act as self signals instead of acting as inter-cell interference. As a result, the same effect as multipath fading is produced, and thus a frequency diversity gain and a macro diversity gain can be obtained. On the other hand, a unicast service is a service in which a user equipment (UE) accesses to a BS to transmit/receive data from/to the BS. In a specific cell, only the unicast service may be provided, or the MBMS may be provided together with the unicast service, or only the MBMS may be provided. When only the MBMS is provided, it is called a dedicated MBMS.
In a wideband code division multiple access (WCDMA) system, synchronization signals are transmitted through a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH). The UE can obtain slot synchronization by using a primary synchronization signal (PSS) transmitted through the P-SCH. The UE can obtain frame synchronization by using a secondary synchronization signal (SSS) transmitted through the S-SCH. System configuration information is transmitted through a physical broadcast channel (P-BCH).
The UE performs synchronization through the P-SCH and the S-SCH in an initial cell search procedure which is initially performed after power is on and a non-initial cell search procedure which performs handover or neighbor cell measurement.
Thereafter, the UE obtains basic system information which is broadcast through the P-BCH. A service provided in a cell may be a unicast service or a dedicated MBMS. A reference signal used in the unicast service has a different structure from that used in the dedicated MBMS. The UE cannot know whether the service provided in the cell is the unicast service or the dedicated MBMS, and thus performs blind detection by estimating channels for both a unicast reference signal and a dedicated MBMS reference signal in a P-BCH decoding process. As a result, an operation time required for obtaining system information by the UE is delayed.
Accordingly, there is a need for a method capable of effectively obtaining a synchronization signal and system information in a wireless communication system in which a unicast service and an MBMS can coexist.